Mannich Reaction, also referred to as amine methylation reaction, is an important organic reaction developed progressively since early 20th century and was named after Germany chemist Carl Ulvich Franz Mannich (1877-1947). Mannich found in 1917 that the reaction of amine hydrochlorides, formaldehyde and C—H acid compounds, in particular ketones, can produce ketone bases. Moreover, substances of characters similar to alkaloids can be produced by appropriate selection of reaction components. Thereafter, a number of research reports were delivered by Mannich school. Specifically, reactions with aliphatic ketones, aromatic ketones and alicyclic ketones as the acid component were intensively investigated, thereby establishing the basis of Mannich reaction. Mannich bases and derivatives thereof were firstly used as medicaments. As time goes on, the products of Mannich reaction are widely spread in various fields of consumer goods production, for example, they can be used for the synthesis of sedative, acesodyne, fungicide, oedema inhibitor, antineoplastic, hepatic protectant, anticoagulant and the like in terms of medicament, and they also found use in terms of explosive, propellant, polymeric flocculant, corrosion inhibitor, vulcanizing accelerator, phytocide, dispersant, antioxidant, active dye, food flavorant, metal chelator.
The application of Mannich bases as corrosion inhibitor started from 1970's. Mannich bases were initially used as preservative in antifreezing solution, and consequently used for treating the inner walls of the reservoir of petroleum gas. As the increase of the well depth in oil exploration and exploitation, and the wide use of technique for increasing the production of crude oil by oil well acidification, the need for high temperature acidizing corrosion inhibitor causes the popularizing of the application of Mannich base type corrosion inhibitor.
Documents and patents related to Mannich base type corrosion inhibitor are mainly:
Xiaoyun Duan and Pengjiang Li synthesized Mannich base type corrosion inhibitors by means of Mannich reaction using formaldehyde, cyclohexylamine and acetophenone as the primary raw materials, and investigated the effect of the ratio of formaldehyde, cyclohexylamine and acetophenone on the corrosion inhibition property of the synthesized Mannich base type corrosion inhibitor (Xiaoyun Duan and Pengjiang Li, Synthesis of a Mannich Base Inhibitor, Technology & Development of Chemical Industry, 2008, 37(9), 11-12); document “Synthesis and Performance Evaluation of YZ-1 Acidizing Corrosion Inhibitor” reported a Mannich base acidification corrosion inhibitor YZ-1 synthesized via Mannich reaction with formaldehyde, acetone and ethylenediamine as the raw materials. The corrosion inhibitor YZ-1 exhibits good inhibition in hydrochloric acid, hydrofluoric acid and mud acid, and tolerates a temperature up to 150° C. (Haihong Zheng, Jianbo Li, Zhibing Mo et al., Synthesis and Performance Evaluation of YZ-1 Acidizing Corrosion Inhibitor, Corrosion & Protection in Petrochemical Industry, 2008, 25(4), 8-10); Faguo Tian, Jianbo Li, Zilin Yan et al. of Southwest Petroleum University prepared Mannich base via Mannich reaction with formaldehyde, acetophenone and ethylenediamine as the raw materials, followed by quaternization with benzyl chloride to obtain Mannich base quaternary ammonium salt. The resulting corrosion inhibitor exhibits good solubility in acid and good compatibility with other acidizing additives, and is non-toxic and resistant to high temperature, and exhibits good corrosion inhibition in different acid solutions (Faguo Tian, Jianbo Li, Zilin Yan et al., Preparation and Performance Evaluation of a novel high temperature acidizing corrosion inhibitor SYB for oil well, Chemical Engineering of Oil & Gas, 2009, 38(5), 426-429); paper “Study and Development of a Mannich Based Corrosion Inhibitor for Hydrochloric Acid acidifying” reports a low cost Mannich base developed using cyclohexylamine. The Mannich base can be used as the primary inhibitor of acidizing corrosion inhibitor for oil gas well. The corrosion test indicates that only 0.5% of the Mannich base is required to be added into 20% industrial hydrochloric acid at 60° C. to satisfy the requirement of first grade acidizing corrosion inhibitor in the industrial standard for petroleum and gas (Jingguang Wang, Hongjiang Yu, Qianding Li, Study and Development of a Mannich Based Corrosion Inhibitor for Hydrochloric Acid acidifying, Journal of Xi'an Shiyou University (Natural Science Edition), 2007, 22(3), 77-79); Chinese patent CN 100577877C discloses a method for synthesizing Mannich base steel corrosion inhibitor mother liquor and steel corrosion inhibitor mother liquor. Steel corrosion inhibitor is prepared by Mannich reaction of secondary amine, aldehyde and alkyl, cycloalkyl, aryl or haloalkyl, cycloalkyl and aryl ketone in aqueous medium; CN101451242A “High temperature acidified corrosion inhibitor for oil passageway containing Cr” discloses an acidified corrosion inhibitor, whose main agent A comprises the following compositions: 25 to 35 parts of quinoline quaternary ammonium salt or quinoline derivate quaternary ammonium salt, 5 to 10 parts of potassium iodide, and 40 to 60 parts of organic solvent methanol or formaldehyde, and an addition agent B comprises the following compositions: 30 to 50 parts of Mannich base, 15 to 35 parts of propiolic alcohol, 5 to 15 parts of chromic chloride, and 20 to 35 parts of formaldehyde. During use, the proportion of A to B is 2-1.5:1; CN 1761715A synthesizes Mannich base curing agents of epoxide or polyurethane system from phenolic compound, formaldehyde and at least one polyamine. An excess of amine is used, so that the phenolic compounds react as completely as possible and are not left to make the product less environmental friendly. CN101182296A also reports a curing agent for epoxy or polyurethane system, prepared from cyclohexanone dimer, formaldehyde and at least one polyamine, with the amine used in excess.
The raw materials for synthesizing Mannich corrosion inhibitors in prior art are primarily (1) ketone, mainly aliphatic ketone such as acetone, butanone, pentanone, hexanone and the like), cycloalkanone such as cyclohexanone, and aromatic ketone such as acetophenone; (2) aldehyde, generally formaldehyde or polyformaldehyde; (3) amine, mainly aliphatic amine such as diethanol amine, dimethylamine, diethylamine, ethylenediamine, aliphatic polyamine, naphthenic amine such as cyclohexylamine, morpholine and the like, aromatic amine such as aniline, benzylamine, aromatic polyamine and the like. The ratio of ketone, aldehyde and amine (monamine) in prior art is 1:1:1 or the ratio of ketone, aldehyde and amine (diamine) is 2:2:1, and thus the resulting Mannich base has a linear structure:

I: primary, secondary amine or ammonia
II: formaldehyde or other aldehydes
III: compound comprising one or more active hydrogen
IV: Mannich base
Z: electron-withdrawing group
The adsorption center of the linear Mannich corrosion inhibitor is located at one end or both ends of the molecule. When the linear Mannich corrosion inhibitor encounters metal wall surfaces, it exhibits terminal group adsorption with one end containing adsorption center forming chemical or physical adsorption with the metal while the other end extending outwards to form hydrophobic layer. The disadvantage of the linear Mannich corrosion inhibitor forming film on the metal surface lies in the low cohesion, low film strength, bad film compactness and bad corrosion inhibiting capability due to single-point adsorption between the corrosion inhibitor and the metal wall surface. In particular, the linear Mannich corrosion inhibitor is difficult to form or cannot form film on corroded or unsmooth metal wall surfaces.

The adsorption of linear Mannich corrosion inhibitor on metal surface